1. Field of the Invention
The present invention generally relates to a method for preparing silicon-on-insulator (SOI) material, and more particularly to a method for preparing a semiconductor substrate with an insulating buried layer by a gettering process.
2. Description of Prior Art
With miniaturization of feature sizes of integrated circuits, it is important to control defects in single crystal silicon. The defects in silicon wafers mainly come from two aspects. In one aspect, grow-in defects, such as crystal originated particles (COPs), are produced during crystal growth processes. In the other aspect, defects are produced when performing heating treatments on the silicon wafers, such as oxygen precipitation. If these defects are positioned in active regions on surfaces of the silicon wafers, performance of devices is deteriorated and the devices are failed. Furthermore, when the silicon wafers are processed and the integrated circuits are manufactured, they are inevitable to be polluted by metals, such as Cu, Ni, Fe and so on. These metal impurities diffuse fast in the silicon. If the metal impurities exist in the active regions of the devices, the devices are failed. Accordingly, it is quite important to effectively remove the metal impurities on the surfaces of the silicon wafers. The oxygen precipitation and induced defects thereof may be served as gettering points for gettering the metal impurities, such that the metal impurities are collected in the defects. But if the oxygen precipitation and the induced defects occur in the active regions of the devices, electrical performances of the devices are affected as well. Accordingly, on the one hand, the oxygen precipitation is required to be produced in the silicon wafers for achieving a gettering function in device technology, but on the other hand, it is hoped that the oxygen precipitation does not occur in the active regions of the silicon wafers. These are basic ideas of internal gettering. In the internal gettering technology of the silicon wafers, denuded zones (DZ) with low oxygen and low metal are formed on the surfaces of the silicon wafers by the heating treatments, and the oxygen precipitation and the induced defects are formed inside the silicon wafers for gettering the metal impurities. After the DZ technology processes are performed on the silicon wafers, the devices are prepared in the DZ and yields of the devices may be effectively increased.
Furthermore, thick-film SOI materials (a top silicon layer is usually greater than 1 μm) are widely applied to high-voltage power devices and microelectromechanical system (MEMS) fields and have rapid development especially in automotive electronics, displays and wireless communications. Since control and conversion of power, automotive electronics and power consuming devices have high requirements for harsh environment, high temperature, high current and high power, the SOI devices must be utilized based on strict requirements of reliability. Currently, users of the thick-film SOI materials mainly comprise Maxim USA, ADI, TI (USA), NEC Japan, Toshiba, Panasonic, Denso, TI (Japan), FUJI, Omron, Philips European and X-Fab. Among the users of the thick-film SOI materials, a lot of applications mainly come from driving circuits in the applications. For instance, the main applications of Maxim are amplifying circuits in mobile receivers, The main applications of Panasonic, TI, FUJI, Toshiba and NEC are scan driving circuits in display driving circuits. The applications of DENSO are automotive electronics and wireless radio frequency circuits. The applications of Toshiba are power control circuits in air conditionings. The applications of Omron mainly comprise sensors. The applications of ADI mainly comprise high-temperature circuits and sensors. The applications of Phillips mainly comprise LDMOS in power devices for consuming electronics, such as car stereos and audio amplifiers. The applications of Magnchip (Hynix) in Korea comprise display driving circuits in digital cameras produced for Kopin and display driving circuits in PDPs produced for LG.
However, since a buried oxide layer exists in the SOI material exists, oxygen elements are externally diffused after the heating treatments and the oxygen elements in the top silicon layer are increased. Accordingly, traditional gettering processes are not suitable for the SOI materials, and the DZ regions do not exist in the top silicon layer, such that the device yields by utilizing the SOI materials are relatively low.